Recent molecular studies into the microbial diversity of the human intestine reveal a much greater diversity than previously recognized and very little is currently known of the contribution of individual groups to the human organism (Gill et al., 2006, Science, 312:1355-1359). One numerically dominant group of microbes, the bifidobacteria, is often suggested to be associated with good intestinal health given their overriding dominance in the feces of breast fed infants (Yoshioka et al., 1983, Pediatrics, 72:317-321). This phenomenon led to their discovery in 1899 by the pediatrician Henri Tissier and his subsequent use of these bacteria for the treatment of infantile diarrhea (Tissier, 1906, Crit Rev Soc Biol, 60:359-361). The proposed beneficial effect of bifidobacteria is further supported by the decrease of these bacteria in geriatric individuals and the concomitant increase of other microbial groups, most notably clostridia and E. coli (Mitsuoka et al., 1973, Zentralbl Bakteriol [Orig A], 223:333-342, Hopkins et al., 2001, Gut, 48:198-205, Ishibashi et al, 1997, Mal J Nutr, 3:149-159). This has led to the growing worldwide interest of including bifidobacteria in foods specifically for their potential intestinal health benefits (O'Sullivan, Primary Sources of Probiotic Cultures, In: Probiotics in food safety and human health. Edited by Goktepe et al., Boca Raton: Taylor & Francis/CRC Press, 2006:91-107). However, clinical feeding studies with bifidobacteria show that while the strains can be detected in subject's feces during feeding trials, they are rapidly lost upon cessation of the studies pointing to a possible loss of competitive fitness of the strains for competition within the human intestinal environment (O'Sullivan, Primary Sources of Probiotic Cultures, In: Probiotics in food safety and human health. Edited by Goktepe et al., Boca Raton: Taylor & Francis/CRC Press, 2006:91-107, Fukushima et al., 1998, Int J Food Microbiol, 42:39-44, Su et al, 2005, FEMS Microbiol Lett, 244:99-103. This may be due to attenuation of the strains, as the fermentation environment is very different to the buffered and anaerobic environment of the human colon.
Bacteriocins are peptide based antimicrobial compounds produced by many types of bacteria and are inhibitory to closely related bacteria. Frequently, the inhibitory spectrum is within the genus of the producing bacterium. A lantibiotic is a type of bacteriocin that has a wide inhibitory spectrum and is also post-translationly modified. Specifically, modification enzymes modify some amino acids into lantionine residues. Nisin, which is produced by certain strains of the lactic acid bacterium Lactococcus lactis, is a lantibiotic with the widest inhibitory spectrum of any lantibiotic described to date that extends to most gram positive bacteria. Given its broad spectrum it is widely used as a preservative and a shelf life extender. Unfortunately, spoilage and pathogenic bacteria are not just gram positive. Many pathogens, such as E. coli and Salmonella are gram negative and many spoilage bacteria are also gram negative, such as Pseudomonas and Klebsiella. 